harris.rar_harris 角点_harris角点提取_harris角点检测_角点提取_角点检测算法

% HARRIS - Harris corner detector % % Usage: cim = harris(im, sigma) % [cim, r, c] = harris(im, sigma, thresh, radius, disp) % [cim, r, c, rsubp, csubp] = harris(im, sigma, thresh, radius, disp) % % Arguments: % im - image to be processed. % sigma - standard deviation of smoothing Gaussian. Typical % values to use might be 1-3. % thresh - threshold (optional). Try a value ~1000. % radius - radius of region considered in non-maximal % suppression (optional). Typical values to use might % be 1-3. % disp - optional flag (0 or 1) indicating whether you want % to display corners overlayed on the original % image. This can be useful for parameter tuning. This % defaults to 0 % % Returns: % cim - binary image marking corners. % r - row coordinates of corner points. % c - column coordinates of corner points. % rsubp - If five return values are requested sub-pixel % csubp - localization of feature points is attempted and % returned as an additional set of floating point % coords. Note that you may still want to use the integer % valued coords to specify centres of correlation windows % for feature matching. % % If thresh and radius are omitted from the argument list only 'cim' is returned % as a raw corner strength image. You may then want to look at the values % within 'cim' to determine the appropriate threshold value to use. Note that % the Harris corner strength varies with the intensity gradient raised to the % 4th power. Small changes in input image contrast result in huge changes in % the appropriate threshold. % References: % C.G. Harris and M.J. Stephens. "A combined corner and edge detector", % Proceedings Fourth Alvey Vision Conference, Manchester. % pp 147-151, 1988. % % Alison Noble, "Descriptions of Image Surfaces", PhD thesis, Department % of Engineering Science, Oxford University 1989, p45. % Copyright (c) 2002-2005 Peter Kovesi % School of Computer Science & Software Engineering % The University of Western Australia % http://www.csse.uwa.edu.au/ % % Permission is hereby granted, free of charge, to any person obtaining a copy % of this software and associated documentation files (the "Software"), to deal % in the Software without restriction, subject to the following conditions: % % The above copyright notice and this permission notice shall be included in % all copies or substantial portions of the Software. % % The Software is provided "as is", without warranty of any kind. % March 2002 - original version % December 2002 - updated comments % August 2005 - changed so that code calls nonmaxsuppts function [cim, r, c, rsubp, csubp] = harris(im, sigma, thresh, radius, disp) error(nargchk(2,5,nargin)); if nargin == 4 disp = 0; end if ~isa(im,'double') im = double(im); end subpixel = nargout == 5; dx = [-1 0 1; -1 0 1; -1 0 1]; % Derivative masks dy = dx'; Ix = conv2(im, dx, 'same'); % Image derivatives Iy = conv2(im, dy, 'same'); % Generate Gaussian filter of size 6*sigma (+/- 3sigma) and of % minimum size 1x1. g = fspecial('gaussian',max(1,fix(6*sigma)), sigma); Ix2 = conv2(Ix.^2, g, 'same'); % Smoothed squared image derivatives Iy2 = conv2(Iy.^2, g, 'same'); Ixy = conv2(Ix.*Iy, g, 'same'); % Compute the Harris corner measure. Note that there are two measures % that can be calculated. I prefer the first one below as given by % Nobel in her thesis (reference above). The second one (commented out) % requires setting a parameter, it is commonly suggested that k=0.04 - I % find this a bit arbitrary and unsatisfactory. cim = (Ix2.*Iy2 - Ixy.^2)./(Ix2 + Iy2 + eps); % My preferred measure. % k = 0.04; % cim = (Ix2.*Iy2 - Ixy.^2) - k*(Ix2 + Iy2).^2; % Original Harris measure. if nargin > 2 % We should perform nonmaximal suppression and threshold if disp % Call nonmaxsuppts to so that image is displayed if subpixel [r,c,rsubp,csubp] = nonmaxsuppts(cim, radius, thresh, im); else [r,c] = nonmaxsuppts(cim, radius, thresh, im); end else % Just do the nonmaximal suppression if subpixel [r,c,rsubp,csubp] = nonmaxsuppts(cim, radius, thresh); else [r,c] = nonmaxsuppts(cim, radius, thresh); end end end